Bump actions/checkout from 5 to 6 in the dependencies group

Bumps the dependencies group with 1 update: [actions/checkout](https://github.com/actions/checkout).


Updates `actions/checkout` from 5 to 6
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: dependencies
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -48,7 +48,7 @@ jobs:
     - name: 'Checkout from Git'
       # Can't refer to matrix in job if conditional, so we have to repeat it every step: https://github.com/actions/runner/issues/1985
       if: ${{ !(matrix.experimental && github.event_name == 'pull_request') }}
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: 'Cache Maven repo'
       if: ${{ !(matrix.experimental && github.event_name == 'pull_request') }}
       uses: actions/cache@v4

.github/workflows/pitest.yml

@@ -19,7 +19,7 @@ jobs:
 
     steps:
       - name: Checkout project
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           # important to set a fetch depth of 2. By default the checkout action make no history available
           fetch-depth: 2

.github/workflows/release.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: 'Checkout from Git'
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - name: 'Set up JDK'